Seasonality of precipitation interacts with exotic species to alter composition and phenology of a semi-arid grassland

While modeling efforts suggest that invasive species will track climate changes, empirical studies are few. A relevant and largely unaddressed research question is: how will the presence of exotic species interact with precipitation change to alter ecosystem structure and function? We studied the effects of changes in seasonal timing of precipitation on species composition and resource availability in a grassland community in Colorado, USA. We examined how seasonal precipitation patterns affect the abundance of historically present (native) and recently-arrived (exotic) plant species, as well as soil moisture, nitrogen, and above-ground biomass. Over four years, we applied four precipitation treatments based on climate model predictions for the study area: winter-wet/summer-ambient, winter-wet/summer-dry, winter-wet/summer-wet and winter-dry/summer-wet. Cover of exotic winter-active grasses was greater in winter-wet treatments than in control or winter-dry treatments. Cover of native wa...